The present invention relates generally to the characterization of conductive objects or surfaces, such as, without limitation metal plates, rods, coatings using non-destructive evaluation techniques and in particular using a four-point probe. Measurements of electrical conductivity (or resistivity) are useful in metal sorting, alloy identification, heat-treatment monitoring of aluminum alloys, and detection of flaws which are manifest as a change in the material conductivity, such as thermal damage in aircraft structures. Prior art methods include existing four-point methods for measuring metal conductivity or thickness that use direct current or the use of standard eddy-current instruments for measuring metal conductivity. These types of approaches have limited utility. For example, where direct current is used only a limited number of material properties can be accurately determined. In addition, there are problems with use of too much current, ionic deposition problems, the need for geometric correction factors, and a host of other problems. Standard eddy-current instruments for measuring metal conductivity cannot be used in the case of ferrous metals.